We report here that animals can be protected against lethal infection by Clostridium tetani cells and Bacillus anthracis spores following topical application of intact particles of live or ␥-irradiated Escherichia coli vectors overproducing tetanus and anthrax antigens, respectively. Cutaneous ␥␦T cells were rapidly recruited to the administration site. Live E. coli cells were not found in nonskin tissues after topical application, although fragments of E. coli DNA were disseminated transiently. Evidence suggested that intact E. coli particles in the outer layer of skin may be disrupted by a ␥␦T-cell-mediated innate defense mechanism, followed by the presentation of E. coli ligand-adjuvanted intravector antigens to the immune system and rapid degradation of E. coli components. The nonreplicating E. coli vector overproducing an exogenous immunogen may foster the development of a new generation of vaccines that can be manufactured rapidly and administered noninvasively in a wide variety of disease settings.Noninvasive epicutaneous vaccination without pain, fear, and tissue damage (35, 38) offers distinct advantages over conventional vaccination regimens in that it can be administered by nonmedical personnel and potentially has a higher compliance rate. Administration of vaccines to the surface of skin may also trigger efficient antigen presentation, as the outer layer of skin is more immunocompetent than deep tissue (9, 29). To date, both animals and humans have been immunized against a wide variety of antigens and pathogens by topical application of adenovirus-vectored vaccines (4,17,22,29,35,38) and bacterial toxin-adjuvanted proteins (11-13).To counteract unpredicted disease outbreaks and bioterrorist attacks, vaccines have to be not only safe and efficacious but also amenable to rapid, large-scale production. The Escherichia coli bacterium is fully defined at the molecular level (3) and has proven to be a simple and efficient vector system for the production of exogenous proteins since its first use, which marked the advent of the recombinant DNA era (1, 19). Recombinant plasmid DNA isolated from transformed E. coli vectors is also effective in eliciting an immune response when used as a genetic vaccine (33, 37). We report here that there is no need to biochemically purify recombinant protein or DNA as a vaccine from E. coli vectors. Topical application of intact E. coli particles overproducing pathogen-derived antigens can effectively mobilize the immune repertoire toward beneficial immune protection against relevant pathogens through the controlled activation of an E. coli-targeted defense mechanism in the outer layer of skin. Production and administration of this new class of vaccines are less dependent upon medical resources than any other vaccination regimens. Moreover, this demonstration provides compelling evidence that a cutaneous defense mechanism that rapidly disrupts invading bacterial cells indeed exists along the precarious skin barrier to ward off infections. MATERIALS AND METHODSRecombinant E. c...

cBacillus anthracis is the causative agent of anthrax, and its spores have been developed into lethal bioweapons. To mitigate an onslaught from airborne anthrax spores that are maliciously disseminated, it is of paramount importance to develop a rapidresponse anthrax vaccine that can be mass administered by nonmedical personnel during a crisis. We report here that intranasal instillation of a nonreplicating adenovirus vector encoding B. anthracis protective antigen could confer rapid and sustained protection against inhalation anthrax in mice in a single-dose regimen in the presence of preexisting adenovirus immunity. The potency of the vaccine was greatly enhanced when codons of the antigen gene were optimized to match the tRNA pool found in human cells. In addition, an adenovirus vector encoding lethal factor can confer partial protection against inhalation anthrax and might be coadministered with a protective antigen-based vaccine.